Don't know if this is related to Brennan's Tweet, but here is more information on Iceberg from Anon on last bread.
Project Iceberg
Project Iceberg. FutureCitiesCatapult © 2017.
Project Iceberg — an integrated city data system above and below ground. FutureCitiesCatapult © 2017.
It's well known that a large proportion of an iceberg lies below the surface; the same is true of our cities. When it comes to planning, we often focus on the visible parts of our towns and cities and forget the complex and valuable ground beneath our feet: 'Project Iceberg' is named to remind us not to forget what we can't see.
http://www.bgs.ac.uk/research/engineeringGeology/urbanGeoscience/iceberg/home.html